Conformal block. The \(n\) -point conformal block \(G(x_k,\Delta ;\Delta _i,c)\)  [1]}, [2]}, [3]}, [4]}, [5]} depends on the external conformal dimensions \(\Delta _i\) , on the internal dimension \(\Delta \) , on the central charge \(c\)  and on \(n-3\)  double ratios \(x_k\)  of points. These variables are most conveniently parameterized (in particular, from the point of view of the AGT correspondence) as \(\Delta =(Q-\alpha )\alpha \) , \(c=1+6Q^2\) , \(Q=b-1/b\) , the primary fields can be written in terms of the free field \(\phi (z)\)  as \(V_\alpha (z)= {:}{\rm e}^{i\alpha \phi (z)}{:}\)  and \({:}\ldots {:}\)  denotes the normal ordering.
